The present invention relates to a medical tube for animals, particularly humans. More specifically, the present invention relates to a catheter, an intravenous cannula (hereinafter briefly referred to as cannula), a bougie, and other medical tubes used for the examination, observation, prevention and treatment of diseases, such as conduit tubes for introducing liquids into and out of the body, tubes used for vasodilation and removal of thrombus and embolus, artificial blood vessels, artificial tracheae, and so on.
Medical tubes are, for example, inserted into blood vessels, particularly coronary artery, trachea, oviduct, urinary duct, various organs, and so on for the purpose of injection of liquids, aspiration, or patency of ducts. The catheters recently proposed are equipped with many functions besides the ordinary functions mentioned above, such as an illumination fiber and an image guide for endoscope, and some are even equipped with a flash hole. U.S. Pat. No. 4,846,812 proposes a cannula made of a shape memory polymer.
There are many people who become unpleasant or in some cases, suffer from pain upon insertion of a medical tube into the body, during indwelling thereof in the body and/or upon removal thereof from the body (such unpleasantness and condition of the body are hereinafter generally referred to as "feeling of physical disorder" in the present invention). However, such feeling of physical disorder is considered to be of little significance in conventional medical tubes, and naturally, no measures are taken to avoid the feeling of physical disorder. The cannula disclosed in the above-mentioned US patent ignores this aspect. While said cannula reduces swelling with body fluids by employing a two-layer structure with the inner layer composed of a non-hydrophilic resin, since its constituent material is highly hydrophilic, the cannula cannot prevent swelling on being contacted with blood, etc. after insertion into the body, and has a serious defect in that it increases the feeling of physical disorder. Combined with the restriction on the body which is caused by indwelling of a medical tube in the body, such feeling of physical disorder can give a physical, as well as psychological pain.
In the meantime, the enteral Diet catheter (ED catheter) has been drawing attention in recent years. The ED catheter is indwelled in duodenum via mouth or nose, throat, esophagus, and stomach for the administration of component nutrients, enteral nutrients, and liquid diet. At present, ED catheters made of EVA (ethylene-vinyl acetate copolymer) or silicone are being used. Those made of EVA are stiff and can be inserted easily, but give a strong pain and a strong feeling of physical disorder. On the other hand, those made of silicone are too soft to be easily inserted. Therefore, an ED catheter which can be easily inserted and gives less pain and less feeling of physical disorder during insertion and indwelling is desired.